Self-powered centrifugal separators are well known for separating fluids of different densities or for separating particulate matter from liquids and have long been used in lubrication systems for engines, particularly diesel-powered vehicle engines, as well as in other industrial separation processes.
The principle of operation of such a centrifugal separator is that a housing contains a rotor which is supported therein to spin at high speed about a substantially vertical axis. Fluid from which contaminants are to be removed is supplied to the rotor at elevated pressure along the axis of rotation and is ejected from tangentially directed nozzles into the housing from which it drains to a sump. Thus, the fluid from which contaminants are to be removed also provides the drive for the rotor. As this fluid passes through the rotor, denser contaminant materials or particles are separated therefrom centrifugally and retained in the rotor, typically as a cake adhering to the interior surface of the rotor, which is cleaned or replaced at intervals.
GB 2160796 and GB 2296942 disclose self-powered centrifugal separators of the type which comprises a base, a substantially vertical spindle upstanding from the base, a rotor mounted on the spindle for rotation thereabout by reaction to fluid emission from rotor nozzles, the base having an inlet passage for said fluid and the spindle having an axial bore and outlets therefrom to supply fluid to the rotor from said inlet passage, and a cover mounted on the base and enclosing the rotor. In this type of separator the fluid is supplied at pressure from the base of the housing and flows upwards through the axial bore to outlets near the top of the bore, which is typically a blind bore. A releasable cap is typically mounted at the top of the spindle to secure the cover. Other designs of self-powered centrifugal separators, for example as disclosed in U.S. Pat. No. 4,498,898 and U.S. Pat. No. 4,557,831, have fluid supplied downwards into the top of the axial bore of the spindle.
In respect of such separators used in lubrication systems for engines it is already known to provide a spring biased valve in the inlet flow path of the fluid to shut off flow at low pressure. This is shown in the applicant's earlier EP 1 009 535 where such a valve is provided in an inlet flow passage in the base of the housing at a location prior to flow of fluid upwards into the axis of the rotor. This protects the engine by ensuring maximum supply of lubricating fluid to said engine when the pressure is low by not diverting fluid to the centrifugal cleaning means at such time.